This invention is generally directed to improved processes for reclaiming certain metallic elements, such as selenium, tellurium and arsenic, and more specifically, the present invention is directed to a process for obtaining high purity selenium, from a crude source material, such as a scrap alloy material containing selenium, tellurium, arsenic, and in some instances halogen substances including chlorine. In accordance with the simple direct, economically attractive process of the present invention, there is obtained in one embodiment selenium, in a purity of 99.999 percent, and pollution hazards as present with some prior art processes are eliminated. High purity materials produced in accordance with the process of the present invention are useful as imaging members, particularly as photoconductive members, in electrophotographic imaging systems, especially those where an electrostatic latent image is formed on the imaging member involved.
The art of xerography as presently practiced involves the formation of an electrostatic latent image on a photoconductive imaging member which can be in the form of a plate, a drum, or a flexible belt, for example. Materials commonly selected for the photoconductive member contain amorphous selenium, amorphous selenium alloys, halogen doped amorphous selenium, halogen doped amorphous selenium alloys and the like. These photoconductive substances must be of high purity, that is a purity of 99.999 percent or greater, since the presence of contaminants has a tendency to adversely affect the imaging properties of the photoconductive substances, including the electrical properties thereof, causing copy quality obtained from such devices to be relatively poor in comparison to devices wherein high purity substances are selected. Numerous complex processes are known for obtaining photoconductive substances such as selenium, or alloys of selenium, which processes can be classified as chemical processes and physical processes. Flexible photoreceptor devices containing photoconductive substances, such as selenium, prepared in accordance with these processes have a tendency to deteriorate over a period of time and thus, the selenium or selenium alloy used, for example, must be recovered and recycled, primarily since these materials are costly, and further to avoid environmental pollution. Various methods are available for recovering selenium and its alloys from the substrate on which it is deposited including heat stripping, water quenching, ultrasonics, and bead blasting.
The prior art processes, including the chemical processes for obtaining high purity materials of selenium and selenium alloys, from contaminated source materials containing these substances, involve a number of process steps, and undesirably high temperature distillations. Additionally, in many of these processes, the recycling of reactants is not achieved. In most instances, the prior art processes for recovering selenium, selenium alloys, or other metallic elements from contaminated source materials is complex, economically unattractive, causes environmental contamination in that, for example, vaporous oxides are formed and must be eliminated. Additionally, many of these processes result, for example, in the recovery of selenium, or selenium alloys which nevertheless contain impurities that can over an extended period of time adversely effect the photoconductivity of the selenium.
There is described in U.S. Pat. No. 4,047,973, a method for recovering selenium, or an alloy thereof from the surface of an endless xerographic belt containing a metal substrate having deposited thereon a thin layer of an organic resinous material which is overcoated with a relatively thicker layer of selenium or a selenium alloy, by subjecting the surface of the belt to jets of high water pressure for the purpose of stripping the selenium or selenium alloy without substantially effecting the layer of organic resinous material. According to the disclosure of this patent, subsequent to removal of the water from the slurry, there is obtained substantially pure selenium or an alloy thereof. This is an example of a prior art physical process for recovering selenium or selenium alloys.
Other prior art processes of interest with respect to the process of the present invention to be described in detail hereinafter include U.S. Pat. No. 4,009,249 and 4,007,255.
In the U.S. Pat. No. 4,009,249 patent there is disclosed a process for precipitating stable red amorphous selenium which may contain a halogen, with hydrazine from a solution of selenous acid in methanol or ethanol. The process is accomplished at a temperature of between about -20.degree. C. and the freezing point of the solution selected. The resulting precipitate is maintained at a temperature of about -13.degree. C. to about -3.degree. C. until a red color appears. The patent U.S. Pat. No. 4,007,255 contains a similar disclosure with the exception that there is disclosed a process for producing a stable red amorphous selenium material containing thallium. There is reference in both of these patents to processes for precipitating selenium by reducing selenous acid in an aqueous solution with sulfur dioxide or sulfurous acid as described in British Pat. No. 515,676, and U.S. Pat. Nos. 2,186,085 and 3,130,012. Further it is stated in these patents that a process for precipitating selenium from an aqueous solution of selenous acid with sulfur dioxide, hydroxylamine hydrochloride, or hydrazine sulfate at 6.degree. to 45.degree. C. is described in U.S. Pat. No. 2,860,954.
Moreover there is described in a copending application an improved process for obtaining in high purity photoconductive compositions, including selenium, tellurium, and arsenic which comprises providing a source material, converting the source material into a mixture of corresponding oxides, converting the oxides to pure esters, and subsequently affecting a reduction of the esters. More specifically, there is described in the copending application an improved process for reclaiming or recovering selenium, tellurium, or arsenic, in high purity, 99.999 percent, which comprises providing a source material, such as a scrap alloy containing these elements and other substances, converting this material into a mixture of the corresponding oxides of the elements, reacting the resulting oxides with an alcohol, or a diol, followed by separation of the resulting esters from the reaction mixture, and subjecting, subsequent to purification by distillation, or recrystallization the esters to a coreduction reaction. The invention of the present application is directed to a similar process with the important exception that the formation of the ester is eliminated.
Accordingly, there continues to be a need for improved processes for reclaiming or recovering photoconductive metallic materials, such as selenium, from crude source materials including scrap alloys and virgin compositions containing these elements. Additionally, there continues to exist a need for an improved simple low temperature chemical process for obtaining selenium in high purities from alloys of selenium and tellurium. There also continues to be a need for improved processes for obtaining selenium and other photoconductive elements in high purity, which processes involve a minimum number of process steps, do not require high temperature distillations, and wherein most of the reactants selected for the process can be recycled and reused. Furthermore, there continues to be a need for improved processes for reclaiming and obtaining selenium, in high purity, which processes eliminate pollution hazards associated with some of the prior art processes. More specifically, there continues to be a need for improved processes for obtaining in high purity, selenium, and other photoconductive elements from scrap or virgin alloys containing these elements as well as from scrap or halogen doped alloys. Furthermore, in accordance with the improved processes of the present invention, selenium, can be recovered from scrap or virgin alloys of selenium and arsenic or halogen doped materials containing selenium and arsenic as well as other contaminants.
Also, while numerous processes are known for the preparation and purification of selenium, there continues to be a need for improved processes for reclaiming this material, which process can be accomplished at low temperatures, and wherein there results products of high purity. Additionally, there continues to be a need for improved processes for reclaiming selenium, in high yields from scrap source alloys containing these materials, and other contaminants. Further, there is a need for improved processes for reclaiming photoconductive substances including selenium, by subjecting to a reduction reaction a solution containing selenium oxides. Moreover, there continues to be a need for improved processes for reclaiming photoconductive selenium substances from scrap alloys or virgin alloys containing these substances and halogens, such as chlorine, wherein the halogens are eliminated during the process.